Data terminal system

ABSTRACT

Apparatus and method for analyzing and encoding graphical data into a serial character stream for transmission over a communications system to a remote data terminal where the character stream is decoded to generate a high resolution graphical display of the data. The graphical display is generated on a teletypewriter which has been modified to permit relatively small, positive and negative incremental movements of the typewriter-type carriage and platen in their respective horizontal and vertical directions. The coding scheme includes analyzing the graphical data on an incremental point-to-point basis to determine the quadrant of movement to the next point, the horizontal and vertical increments, and the symbol to be printed. The data is also analyzed to detect information which is invariable over a plurality of points and such information is commanded to be stored in the receiving remote data terminal. Thereafter, only variable information is transmitted to the remote terminal until one of the invariable items of information changes. Alternate apparatus and methods are disclosed for further reduction of the transmission of invariable information and for suppressing the printing of symbols which contain graphing information.

United States Patent [72] Inventors LawrenceJ.Kamm

[54] DATA TERMINAL SYSTEM 23 Claims, 10 Drawing Figs. [52] [1.8. CI.IMO/172.5 [5 I] Int. Cl G061 1/00 [50] Field of Search 340/1725 5 6]References Cited UNITED STATES PATENTS 3,199,111 8/1965 Jennings et a1.340/172.5 X 3,275,989 9/1966 Glaser et al..... 340/1 72.5 3,413,61111/1968 Pfuetze 340/172.5 3,434,113 3/1969 Wiley et al... 340/l72.53,438,003 4/1969 Bryan 340/172.5 3,490,690 1/1970 Apple et a1. 340/172.5X 3,544,972 12/1970 Trousdale 340/172.5

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. 72 0474 FILE %30 70 i W480i REGISTER SVMBOL Primary Examiner-Gareth D.Shaw Assistant Examiner-Sydney R. Chirlin Attarney-Fulwider, Patton,Rieber, Lee & Utecht ABSTRACT: Apparatus and method for analyzing andencoding graphical data into a serial character stream for transmisisgenerated on a teletypewriter which has been modified to permitrelatively small, positive and negative incremental movements of thetypewriter-type carriage and platen in their respective horizontal andvertical directions. The coding scheme includes analyzing the graphicaldata on an incremental point-to-point basis to determine the quadrant ofmovetion is transmitted to the remote terminal until one of theinvariable items of information changes.

Alternate apparatus and methods are disclosed for further reduction ofthe transmission ofinvariable information and for suppressing theprinting of symbols which contain graphing information.

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\J I mag amour FtAb smut tomm tl 106 Bu rs! BACKGROUND OF THEINVENTION 1. Field of the invention The present invention relatesgenerally to data terminal systems and, more particularly, to such asystem which can generate a high resolution graphical display of data aswell as print textual material, all with the same type head.

2. Description of the Prior Art in the field of data processing, it isoften desirable to present the results of computer computations as agraphical display rather than as a tabulation or text. Therefore, manyautomatic plotters have been developed to accept data in digital formfrom a computer and generate a corresponding visual graph. In manycases, additional graphical information such as axes, lines. scales andlabels may also be generated and plotted by the plotter.

Such digital plotters generally have a marking instrument such as a penwhich is moveable over a flat surface along coordinate axes in responseto digital data. in some cases, the marking instrument leaves acontinuous track while, in other devices, a mark is left only atspecified points. Also, for some digital plotters, the marking device isan impact-type printer and one of a limited font of symbols may beprinted at each plotted point.

In some computer applications, such as time-sharing, communication withthe computer is made by means of a data terminal at a remote location.Ordinarily, the users of such data terminals in time sharing computersystems do not have a sufficient amount of data to be processed towarrant the expense of a complete computer system. For many such users,even a relatively inexpensive data terminal is, itself, a substantialinvestment.

in many cases, the data processed through such data ter minals is alsobest displayed in graphical form. While digital plotters of the typediscussed above generally perform quite well in graphing data, they arehighly specialized units and tend to be relatively expensive compared tothe cost of commonly used data terminals. Additionally, the digitalplotter cannot be economically substituted for the data terminal andused to print textual material because of the complex programs needed inthe computer to command a pen or stylus to draw" an alphanumericcharacter. The amount of computer processing to print simple textualmaterial then becomes prohibitively expensive and a great deal of timeis required to generate each alphanumeric character. impact printingplotters usually have a font of printable symbols far too small forprinting text. Thus, for the average user of a time-sharing dataterminal, the ability to both produce a graphical display of data, andprint textual material, is an expensive proposition if a conventionaldata terminal and digital plotter is employed.

Attempts have been made to solve this problem by utilizing theconventional data terminal equipment to produce graphical displays ofdata. Typically, a relatively inexpensive data terminal uses aninput-output device in the form of a modified electric typewriter or aconventional teletypewriter. Such a machine can be used to produce agraphical display by properly programming the computer to command theoperation of the typewriter or teletypewriter to print suitable symbols,such as a period or asterisk, at appropriate points.

However, because of the relatively large and fixed incremental movementsof such machines, the resultant graphical display is of relatively lowresolution. Furthermore, the range of movement of conventionaltypewriters and teletypewriters is somewhat limited. For example, theline feed of such machines usually cannot be reversed, necessitatinganalysis and scanning of the graph to be generated from the top to thebottom. Such computer analysis consumes valuable computer processingtime.

Conventional analysis and encoding schemes for both digital plotters andtypewriters or teletypewriters generally transmit complete informationregarding each new point to be plotted. The results in a great deal ofinvariable information being transmitted. Since a speed limiting factorfor for many data terminal systems using telephone lines is thetransmission rate of the line, the transmission of the invariableinformation results in the graphical display being generated relativelyslowly.

Thus, there has long been a need in the data processing field for a dataterminal system which could quickly, economically and reliably producehigh resolution graphical displays of data as well as print texturalmaterial. The apparatus and method of the present invention fills thisneed.

SUMMARY OF THE INVENTION BAsically, the present invention provides adata terminal system which can produce either conventional text or ahigh resolution graphical display in an efiicient and economical manner.The system of the invention is particularly useful in data processingsystems in which data in a central computer is to be transmitted to, andreproduced at, a remote data terminal, either as printed text, as agraphical display or as a combination of both.

One novel feature of the presently preferred embodiment of the inventionis the use of an output device in the form of a conventionalteletypewriter in which the type carriage and line feed drive mechanismshave been replaced by stepping motors which can incrementally move thetype carriage and platen a distance considerably less than the normalwidth of a space or line, respectively. The points on a graphicaldisplay can, therefore, be placed relatively close together for a highresolution display. Additionally, the stepping motors can be easilyoperated in positive or negative rotational directions to follow thecourse of any curve or plot. The type carriage of the teletypewriterused with the present invention is also provided with anelectromechanical actuator to physically suppress the printing of areceived character which has graphical rather than textual significance.Alternately an electrical print suppress scheme may be used.

Another novel feature of the data terminal system of the presentinvention includes the use of a unique data analyzing and encodingscheme to substantially reduce the number of characters which must betransmitted to a remote terminal for point-to-point movement of the typecarriage and platen of the teletypewriter. The length of the characterstream needed to generate a complete graph is thereby greatly reduced,decreasing the time needed to generate the graph and, consequently, alsodecreasing the cost of the computer time needed when operating in a timesharing system.

The number of characters needed to move the type carriage and platenfrom one point to another is initially reduced by combining both of thepositive or negative signs of the respective horizontal or verticalmovements of the carriage and platen into a single item of informationindicative of one of the four well-known quadrants of conventionalrectangular coordinate axes. Thus, one of the two characters needed totransmit both of the signs is eliminated, reducing the number ofcharacters which must be transmitted.

The number of characters which must be transmitted for each point isfurther reduced by the system of the present invention by analyzing thedata to determine if any of the quadrant, horizontal or verticalincrement, or the symbol to be printed is invariable frompoint-to-point. If so, the invariable information is transmitted to theremote terminal together with an appropriate command signal that suchinvariable information be stored in the remote terminal. Thereafter,only the variable information is transmitted to the remote terminal. Thecomplete information for movement between points is then taken from thestored invariable information and the received variable informationuntil one of the stored items of invariable information changes. Thestored items of information are then appropriately changed. Thus, forsome types of movements of the type carriage and platen, only one of theitems of information needed for point-to-point movement need betransmitted, thereby greatly reducing the length of the character streamand the time required to generate the graph.

In the coding scheme utilized in the graphing data terminal system ofthe present invention, when one or more of the stored invariable itemsof information changes, all of the items of information areretransmitted to the remote terminal with an appropriate storage commandsignal indicative of a particular mode of the operation. To reduce thenumber of characters which must be transmitted in such a case, thecommand signal is combined with the quadrant information to form amode-quadrant character. The mode and quadrant information are thenseparated in the remote terminal.

An additional feature of the coding scheme of the invention is the useof only alphanumeric symbols for all of the graphing as well as texturalinformation. Since substantially all computer systems must accept suchalphanumeric symbols, the graphing data terminal system of the presentinvention is thus compatible with practically any computer system.

The exclusive use of alphanumeric characters results in another novelfeature of the invention. In an alternative coding scheme, thehorizontal and vertical distances are restricted to the numericcharacters only so that an alphabetic character may be simplyinterpreted as a mode-quadrant character.

Thus, in summary, the graphing data terminal system of the presentinvention includes a modified teletypewriter mechanism to permitrelatively small incremental movement of the type carriage and platen ineither positive or negative directions so that typing and plotting canbe accomplished with a single-type head with the printing of receivedcharacters being suppressed when the characters have graphical ratherthan text significance. The length of the character stream needed forpoint-to-point movement is greatly reduced by transmitting a singlemode-quadrant character to set the mode of operation and the quadrant ofmovement. Additionally, the graphical data is analyzed on apoint-to-point basis to determine invariable information which is thencommanded to be stored in the remote terminal and only variableinformation transmitted thereafter.

Other objects and features of the graphing data terminal system of thepresent invention will become apparent when the following more detaileddescription is considered together with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a block diagram of the dataterminal system of the present invention showing the interconnection ofmajor operative elements thereof;

FIG. 2 is a diagrammatic, perspective view of a teletypewriter mechanismshowing the main elements thereof which are modified in accordance withthe present invention;

FIG. 3 is a tabulation of the stored invariable and transmitted variableinformation of the initial character stream for the four modes ofoperation of the system;

FIG. 4 is a representation of the graphing information contained in anillustrative serial character stream for the modes of operation of thedata terminal system of the invention;

FIG. 5 is a block diagram of an illustrative analyzer-encoder forgenerating the character stream to be transmitted to the remote tenninalof the system;

FIG. 6 is a functional block diagram of the presently preferredembodiment of the decoder-controller of the system of the presentinvention;

FIG. 7 is a partial block diagram of an alternative embodiment of thedecoder-controller of the system shown in FIG. 6;

FIG. 8 is a representation of the graphing information contained in anillustrative serial character stream for the alternate embodiment of thedecoder-controller shown in FIG.

FIG. 9 is a diagrammatic perspective view of the main elements of thetype head printing mechanism of a tele typewriter, together with arepresentative electromechanical print suppress mechanism for use withthe graphing data terminal system of the present invention; and

FIG. 10 is a partial block diagram of the decoder-controller shown inFIG. 6 showing an alternative electronic print suppress scheme.

DESCRIPTION OF THE PREFERRED EMBODIMENT Turning now to the drawings,particularly FIG. I thereof, the data terminal system of the presentinvention is designed primarily for use in a time-sharing computersystem with a computer 20 connected to a remote data terminal 22 througha communications system 24. Typically, the communications system 24 is apart of a telephone network, using either dedicated lines or simplevoice grade telephone lines.

Basically, when the presently preferred embodiment of the data terminal22 of the present invention is connected to the computer 20, datainstructions are transmitted to the computer by means of ateletypewriter keyboard 26. However, it should be appreciated that datacan be transmitted by other means, such as a paper tape reader, or thelike. Typically, the computer 20 will be commanded to follow theinstructions of a particular program in a program library 28 which isavailable to users of the computer system. Typically, the programlibrary 28 contains programs for making calculations or processing datasupplied by the user of the terminal. In the system of the presentinvention, when it is desired to present the results of the calculationsor processed data in graphical form, additional instructions are givento the computer to assemble the results in a data file 30. Additionally,data in tabular form may be entered into the computer 20 from the dataterminal 22 for assembly in the data file 30.

Data for printing labels, graphing axes, scales and other informationneeded to generate a complete graph are supplied by conventionalauxiliary programs in the program file 28 and forms no part of thepresent invention. The data file 30, therefore, contains apoint-by-point listing of every point to be plotted on the graphicaldisplay.

An analyzer-encoder 32 then examines each point in the data file 30 inturn and assembles a coded character stream according to a coding schemewhich is a part of the present in vention. Each character of the streamrepresents either graphing information, or text material to be printed,depending on the analysis of the analyzer-encoder 32, as discussedbelow. The character stream is transmitted through the communicationssystem 24 to the data terminal 22 where it enters a decoder-controller34 which generates suitable electrical signals for incrementally movinga teletypewriter mechanism 36 from point-to-point and printing at eachpoint any of the plurality of symbols available in the teletypewritermechanism 36. The teletypewriter mechanism 36 may be commanded to printtextual material or generate graphical displays with equal facility.

A teletypewriter was chosen for the combined printing and graphingmechanism of the data terminal system of the present invention forreasons of economy. However, while a teletypewriter is an excellentlow-speed text printing device, the incremental movements of the typecarriage drive and platen line feed mechanisms are much too large forhigh resolution graphing purposes. Therefore, the teletypewriter of thepresent invention is modified as shown in FIG. 2. The line feed drivefor a platen 38 of the teletypewriter is modified so that it is drivenabout one end 40, through a first belt and pulley arrangement 42 by afirst stepping motor 44. A type carriage 46 of the teletypewriterremains conventionally driven by a second belt and pulley arrangement48. However, a drive shaft assembly 50 of the type carriage 46 ismodified to be driven by a second stepping motor 52 and a third belt andpulley arrangement 54 through a clutch 56. The clutch 56 is selectivelyengageable by means of a conventional solenoid (not shown) so that thetype carriage 46 can be returned to the left margin by means of a spring58.

The type carriage conventionally carries a type head 60 which isselectively driven into contact with a typing ribbon 62 and thence intocontact with a sheet of paper 64 wound around the platen 38. The typingcharacter selection mechanisms of the teletypewriter are not modified inthe system of the present invention.

By proper choice of the first and second stepping motors 48, 52 and thefirst and third belt and pulley arrangements 42, 54, respectively, theplaten 38 and type carriage 46 may be moved relatively small incrementaldistances in either positive or negative directions for each fixedincremental rotation of the motors. In the presently preferredembodiment of the invention, each incremental movement was chosen as0.02 inches. This value was chosen so as to be able to print asubstantially continuous line with the smallest symbol which could beprinted, the period Thus, it can be seen that a high resolution graphcan be generated using the stepping motors.

The maximum number of increments between points in either the horizontalor vertical directions of the type carriage 46 or platen 38respectively, (hereinafter called a step") was set at so that themovements could occur and the symbol printed before the next characterarrived at the data terminal 22. It should be appreciated that theincrement spacing and step size can be chosen to fit particular computersystems and data terminals.

In the system of the present invention, the data in the data file 30 isanalyzed on a point-to-point basis so that the horizontal and verticalmovement information is representative of the incremental distancebetween points, as opposed to the respective distances from some fixedreference lines. Thus, the horizontal and vertical incremental distancesfrom a current point to a new point (designated dX and a'Y,respectively, according to convention) are in the incremental formrequired by the drive mechanisms of the stepping motors 44, 52 so thatfurther analysis or calculation within the data terminal 22 isunnecessary. The dX, dY and symbol information is then converted tosuitable coded characters, such as the American Standard Code forInformation Interchange (ASCII), which can be transmitted to the dataterminal 22 over the communications system 24.

It should be appreciated that there is no feedback from the receivingdata terminal 22 to the analyzer-encoder 32 of FIG. I so that commandedmovements of the type carriage 46 and platen 38 are assumed to havetaken place. The incremental movement from point-to-point and theopen-loop type of operation greatly simplifies the system of theinvention for economy.

It will be understood that five separate items of information arerequired to move from a current point on the graph to a new point andprint a symbol. In particular, the sign and value of the horizontalincrement, the sign and value of the vertical increment and the symbolwhich is to be printed are all necessary.

In the data terminal system of the present invention, one of these fiveitems of information is eliminated by referencing the signs of thehorizontal and vertical increments dX and dY, respectively, to thewell-known four quadrants of conventional rectangular coordinate axes.The sign information of both dX and W is combined into a single item ofquadrant information, thereby eliminating one transmitted character foreach point-to-point movement. It will be appreciated that thissubstantially reduces the length of the character stream needed togenerate the entire graphical display. This not only greatly increasesthe speed in which a graph can be generated, but also substantiallyreduces the cost of the computer processing time in time sharingsystems.

Additionally, it will be appreciated that, for particular types ofgraphing or text printing operations, a number of the items ofinformation may remain invariable over a plurality of points. Forexample, it can be seen that if the terminal is to print textualmaterial, the signs of both dX and H between printed symbols isinvariable over an entire line of text, the spacing (dX) between theprinted symbols is invariable and the vertical movement (a'Y is zero sothat d! is also invariable. Thus, the only item of information whichvaries from point-to-point is the symbol which is to be printed.

In the data terminal system of the present invention, great advantage istaken of the fact that certain of the items of information remaininvariable for a plurality of points by transmitting the items ofinvariable information to the data terminal only once and commandingtheir storage therein. Thereafter, only the items of variableinformation for each point are transmitted to the data terminal. Thefive necessary items of information needed for movement frompoint-topoint are then taken from both the received variable informationand the stored invariable information. Thus, in the above example, thequadrant information, the dX information and the dY information would betransmitted to the data terminal and stored. Thereafter, each receivedcharacter would represent only the symbol to be printed. For the citedexample, it can be seen that only one of five items of information needbe transmitted for each point once the invariable information is storedin the data terminal. The coding scheme of the present invention therebygreatly decreases the length of the character stream for speed andeconomy, as discussed above.

The data terminal of the system is commanded to store particular itemsof information by means of one of four mode signals generated by theanalyzerencoder of FIG. 1. The mode signals indicate the four modes ofoperation of the system of the invention. The characteristics andadvantages of the four operating modes are discussed below.

Whenever any of the items of stored information changes, the completecombination of quadrant, dX, dY and symbol information is retransmitted,with the appropriate changes, to the data terminal 22. In order todecrease the number of characters which must be transmitted to the dataterminal, the appropriate mode signal is advantageously combined withthe quadrant information to form a single transmittable modequadrant(abbreviated mode-quad or mode/quad in the drawings) character. Thereceived mode-quadrant character is separated into its mode and quadrantcomponent pans in the decoder-controller 34 of the data terminal 22 ofFIG. 1.

FIG. 3 illustrates, in tabular form, the format of the stored invariableand variable information for the four modes of operation of the system.The printing of textual material, discussed above as an example, isdesignated as mode I for the presently preferred embodiment of theinvention. Additionally, three other modes are provided for othercommonly encountered operating conditions in graphing operations.

As another example of a mode of operation, if a curve is to be printedwhich is slowly varying in the vertical direction for equal horizontalincrements, the quadrant, the dX value and the symbol (perhaps a periodto be printed will be invariable over the curve. As will be seen from aconsideration of in FIG. 3, the proper mode of operation would be mode 2in which the received mode-quadrant, (IX and symbol characters arestored leaving a'Y as the only variable.

As seen in FIG. 3, the variable character for mode 3 is dX and, for mode4, both the dX and the (N characters are designated as variables. Mode 3might be used, for example, when the graph is based on equal verticalincrements rather than the previously considered equal horizontalincrements and mode 4 might be used when a relatively smooth curve isbeing generated which is moving in the same quadrant but which hasvariable dX and dY values, or when the proper mode has not yet beendetermined.

As discussed above, when any of the items of stored information change acomplete character sequence consisting of the mode-quadrant, dX, dY andsymbol characters is transmitted to the data terminal 22. The firstcharacter received, the mode-quadrant character, is stored andconditions the decoder-controller 34 (FIG. 1) to store the appropriatesubsequently received characters, depending on the mode of operation.Thereafter, the only characters which are trans mitted to the dataterminal 22 are the characters designated as variable for the particularmode. The data tenninal 22 then moves the type carriage 46 and platen 38to a new position and prints a symbol in accordance with the receivedvariable information and the stored invariable information.

In the presently preferred embodiment of the invention, the onlytransmitted characters which have significance as modequadrant, dX, dYand symbol information are the alphanumeric characters, and theirsignificance depends on their posi tion in the initial character stream.Once the initial character stream is stored, however, the data terminalcannot distinguish between received characters as being variables orpart of a new character stream to be stored. Thus, in one embodiment ofthe system of the present invention, a special character which is notalphanumeric, called the flag character transmitted to the data terminal22 to condition the terminal to receive the next four characters asmode-quadrant, dX, dY and symbol characters and store the appropriatecharacters depending on the mode of operation. The flag character may beany nonalphanumeric character which can be handled and generated withinthe particular computer used with the present system. Because theAmerican Standard Code for Information Interchange (ASCII) isextensively used in timesharing applications, a character commonly usedin this code, the up arrow," is designated to serve as the flagcharacter in the presently preferred embodiment of the invention. Itshould be noted, however, that any nonalphanumeric character can servethe same function, depending on particular computers and applications.

The particular character stream combinations for entering the variousmodes are illustrated in FIG. 4. For mode 1, for example, the i'irstreceived character is the flag character which conditions the dataterminal 22 of FIG. 1 to attach special significance to the next fourreceived characters. Therefore, the second character to be received isthe mode-quadrant character which is stored and thereafter conditionsthe data terminal 22 to store the next two received characters as the dXand dY values, respectively. Following the receipt and storage of thethird and fourth characters, the 4X and dY values, respectively, thefifth received character indicates the symbol to be printed. The nextreceived characters, the sixth, seventh, eighth and ninth characters,are all interpreted by the data terminal as symbols to be printed. ThedX, (N and quadrant information needed for movement to the new point areall taken from the previously stored characters.

For mode 2, the variable is the dY value and, following the receipt ofthe flag character, the mode-quadrant character conditions the dataterminal to store the dX and symbol characters, but treats the dYcharacter as a variable. Therefore, following the receipt of the fifthsymbol character, the data terminal interprets the sixth, seventh,eighth, and ninth character as variable :1! values and the type carriage46 and platen 38 are moved accordingly. The same stored symbol is thenprinted following each movement.

For mode 3, the dX value is treated as a variable, as discussed above.Therefore, following the receipt of the flag character, themode-quadrant, dY, and symbol characters are stored and the dX characteris treated as a variable. The sixth, seventh, eighth and ninth receivedcharacters are then received as variable dX values.

For mode 4, both dX and dY are treated as variables, as discussed above.Therefore, following the receipt of the flag character, only themode-quadrant and symbol characters are stored and the sixth, seventh,eighth and ninth received characters are alternately treated as dX anddY values.

It should be appreciated that once a flag character is received and theappropriate characters are stored, the system remains in that particularmode until at least one of the stored characters must be changed. Then,another flag character is generated and the stored information ismodified accordingly.

It can also be seen that once the invariable information is stored, amovement of the type carriage 46 and platen 38 to print a symbolrequiring five items of information can be accomplished with thetransmission of only one character instead of five, if the system is inmodes 1, 2 or 3, and with only two transmitted characters for mode 4. Itwill be appreciated that a high resolution graph normally contains aconsiderable number of points, when the axes and scales are consideredand, when voice grade telephone lines are used, the graphicalinformation must be transmitted relatively slowly. Therefore, if allfive items of information had to be transmitted to move from one pointto the next, the graph would be generated quite slowly. Thus, if anumber of points can be graphed by transmitting only one character foreach point, as can be done with the data terminal system of the presentinvention, the graph can be generated much faster and more economically.

In the presently preferred embodiment of the invention, the analyzingand encoding operation of the analyzer-encoder 32 of FIG. 1 ispreferably accomplished by means of a series of programmed steps withinthe computer 20, as opposed to separate hardware. While a wide varietyof programs and schemes may be used to analyze and encode the graphicaldata, an illustrative block diagram of the basic operation of theencoder-analyzer 32 is shown in FIG. 5. Basically the encoder-analyzerexamines each point in turn and compares it with the state of the storedcharacters in the data tenninal 22. If one of the stored characterschanges, the analyzer-encoder 32 generates a complete character streambeginning with a flag character. If the stored characters are the same,only the item of information treated as a variable is transmitted.

Generally, graphical and textual data contained in the data file 30 isselected on a point-to-point basis by a sequential point selector 66which then transfers the coordinate information to a comparator 68 andthe symbol information to a symbol register 70. The coordinates of thepreviously examined point are the coordinates of the current position orpoint of the graph and are stored in a current point coordinate register72 after passing through a suitable time delay network 74 connected tothe sequential point selector 66. The coordinates of the new point arethen compared with the coordinates of the current point. The quadrant ofmovement is determined and transferred to a quadrant register 76, theincremental X axis difference (dX) between the two points is determinedand transferred to a dX register 78 and the Y axis difference (dY isdetermined and transferred to a W register 80.

According to the coding scheme of the present invention, the quadrant,dX, (N and symbol information for the new point to be plotted is thencompared with the corresponding information which is stored in thereceiving data terminal for a particular mode of operation to determinewhether a change in the stored information is necessary. As discussedabove, there is no feedback between the analyzer-encoder 32 and thedecoder-controller 34 of FIG. 1. Therefore, duplicate quadrant, dX, (Nand symbol storage registers 82, 84, 86 and 88, respectively, areprovided in the analyzer-encoder to duplicate the stored information inthe decoder-controller 34.

Each of the quadrant, dX, (N and symbol information for the new pointcontained in the registers 76, 78, 80 and 70, respectively, is thencompared by means of a comparator with the information in thecorresponding storage registers 82, 84, 86 and 88, respectively, todetermine whether the stored information in the decoder-controller 34has to be changed. For example, if the quadrant information entered inthe register 76 is different than the quadrant information stored in thequadrant storage register 82, the comparator 90 sends a signal to amode-quadrant controller 92. The controller 92 then signals a pluralityof mode-quadrant change gates 94 to gate the new quadrant informationthrough the change gates 94 to the quadrant storage register 82. In thesame manner, the dX, dY and symbol information is compared with thestored information and the stored information is changed if necessary.It should be noted that differences between the variable item ofinformation for the particular mode of operation and the storedinformation for that item does not cause the mode-quadrant controller tochange the stored information.

The mode quadrant controller also signals a flag signal generator 96, amode-quadrant signal generator 98, and dX, dY, and symbol gages 100,102, 104, respectively, to selectively gate the information in thequadrant, dX, dY and symbol registers 76, 78, 80 and 70, respectively,to a character assembier 106. Which of the 11X, dY and symbol gates 100,102, and

104, respectively, are enabled depends on the particular mode ofoperation. The character assembler 106 provides a proper sequentialoutput 108 to the computer output buffer for transmission to the dataterminal 22, as discussed above. It should be noted that, if none of thestored information has to be changed, the mode-quadrant controller 92enables only the dX, dY or symbol gate 100, 102, 104, respectively,which is as sociated with the information which is considered variablefor the particular mode in which the system is operating.

As discussed above, the illustrated analyzing and encoding scheme shownin MG. is only representative of the type of data analyzing and encodingneeded to generate the desired character stream. Additionally, it willbe appreciated that the analysis and encoding for the presentlypreferred embodiment of the invention is accomplished by means of ananalytical method suitable for implementation as a program within thecomputer itself. A suitable method for encoding the data in the datatile '5 described in copending U.S. Pat. application Ser. No. 20,494,filed on Mar. 18, 1970 entitled METHOD OF ENCODING GRAPHICAL DATA, andinvented by George Kurata. Reference is made to this copendingapplication for further details concerning the actual scheme ofanalyzing and encoding in the data file.

An illustrative block diagram of the presently preferred embodiment ofthe decoder-controller 34 of FIG. 1 is shown in FIG. 6. Generally, thecharacters received from a communications line 108 are serially enteredinto a conventional input register 110 at a relatively slow speed.Thereafter, the character is processed in parallel through thedecoder-controller 34 at a relatively high speed. When the serialreceipt of a character is completed, the equivalent of a "clock" signalis generated, through conventional circuitry within the input register110, which initiates and controls the parallel processing of thecharacter through the decoder-controller 34.

The operation of the decoder-controller 34 is best described by means ofa series of examples. First, assume that the received character is not aflag character and that the system is properly operating in a particularmode. The received character in the input register 110 is then treatedas the variable item of information and is fed to respective dX and dYselection gates 112 and 114, respectively, via a general input line 116.Additionally, the inputs from the communications line 108 is feddirectly on a serial input line 118 to symbol selection gates 120. Theinputs to the JK and d\ selection gates 112 and 114, are thus inparallel while the inputs to the symbol selection gates 120 are inserial form. This difference is due to the fact that theteletypewriter-type head mechanism requires a serial data input.

Depending on the operating mode, one of the three selection gates 112,114, 120 is enabled to feed the received character in parallel to an Xor a Y actuator 122, 124, respectively, or serially to a symbol actuator126. The remaining two of the three selection gates 112, 114 and 120 areenabled to feed a character stored in either a first or second storageregister 128, 130, respectively, depending on the operating mode. In thepresently preferred embodiment of the invention, the JK and (H selectiongates 112, 114 may receive inputs from either the first or secondstorage registers 128, 130, respectively. However, the symbol selectiongates 120 must receive data in serial form and a single parallel toserial converter 132 is connected to the output of the first storageregister 128 only. The symbol selection gates 120 can then receive theproper serial inputs from only the first storage register 128. A serialoutput of the converter 132 is thus fed to the symbol selection gates120 via a line 134.

The X and Y actuators 122, 124 are conventional devices for operatingthe stepping motors 44 and 52 discussed above with reference to FIG. 2.The symbol actuator 126 includes the electromechanical mechanismsprovided within the teletypewriter itself together with any requiredconventional matching circuitry. The dX, dY and symbol selection gates112, 114 and 120 are selectively enabled by means of mode signals from amode storage selection 136 which has four out puts combined for clarityin FIG. 6 into a single mode signal line 138. The mode signals areapplied to control inputs 140, 142 and 144 associated with each of therespective selection gates 112, 114 and 120. It should be understoodthat the dX, if! and symbol selection gates 112, 114 and 120, as well asthe control inputs 140, 142 and 144, are conventionally designed logicgating networks. Also, the first and second storage registers 128 and130, as well as associated control inputs 146 and 148 for theseregisters, are conventionally designed.

As a second example, assume that one or more items of the storedinformation is to be changed. The incoming character streams for thefour modes of operation would then be in the orders shown in FIG. 4.

A flag character is serially read into the input register and itspresence is detected by flag detector 150, in the form of conventionallogic gates, which resets a mode-quadrant change sequence counter 152.The sequence counter 152 is conventionally designed and controls thestorage of the subsequently received characters, depending on the mode.Therefore, the counter 152 generates P1 through P5 signals in sequencewith subsequently received characters. When the counter 152 reaches theP5 signal, all characters received thereafter are designated asvariable. The P5 signal conditions the JK and dY symbol selection gates112, 114 to accept inputs from either the general input line 116 or oneof the first and second storage registers 128, 130, respectively,depending on the mode of operation. The P5 signal also conditions thesymbol selection gate to accept inputs from either a serial input line118 or the first storage register 128 through the parallel to serialconverter 132.

[n the presently preferred embodiment of the invention, particulargroups of the alphanumeric characters are chosen to representmode-quadrant, dX, JV and symbols. The accuracy of the incoming streamcan be at least partially checked by means of a character verifier 154which examines the character on the general input line 116 with respectto the P1 through P4 signals from the sequence counter 152 to determineif the proper types of characters are received in the proper sequence.If not, an output 156 inhibits the sequencing of the sequence counter152 and further disables any operation on the received incorrectcharacter.

When the mode-quadrant character is received, the counter 152 generatesthe P1 signal which enables a mode quadrant decoder 158 to separate thequadrant and mode information. The quadrant information is fed over aline 160 to a quadrant storage section 162 which controls the X and Yactuators, 122, 124, for movement in the proper positive or negative Xand Y directions. The mode information is fed over a line 164 to themode storage section 136 which conventionally generates mode signalsindicative of a particular mode, as discussed above.

Because it is possible for the incoming mode-quadrant character to passthrough the symbol selection gates 120 to the symbol actuator 126 wherea meaningless alphanumeric symbol would be printed, a print suppresssection 166 is provided to selectively inhibit the operation of the typehead mechanism of the teletypewriter. The print suppress section 166 hasassociated control inputs 168 which receives disabling inputs from theP4 and P5 signals only. Thus, any character received by the symbolactuator 126 through the symbol selection gates 120 while themode-quadrant, (Di and dY characters are being received will not beprinted.

The mode signals on the mode signal line 138 are fed to the controlinputs 146, 148 of the first and second storage registers 128, 130,respectively, to condition the registers to store the appropriatesubsequently received characters when the registers are enabled by theappropriate signals from the sequence counter 152. The mode signals arealso fed to the (bi, a'Y and symbol selection gates 112, 114, 120 tocondition the gates to feed either the general input line 116, theserial input line 118 or the characters stored in the first and secondstorage registers 128, to the respective actuators 122, 124 and 126,depending on the mode.

It should be noted that, since the quadrant information is stored in thequadrant storage section I62, only two of the three remaining items ofinformation, dX, W and the symbol, can be stored in the first and secondstorage registers I28, 130 because one of the items serves as a variablefor modes 1, 2 and 3. For mode 4 only the symbol is stored because bothdX and dY are treated as variables. In the decoder-controller 34 of thepresent invention, the symbol is always stored in the first storageregister 128, as discussed above. Therefore, for mode 2, the n'Xcharacter is stored in the remaining second storage register I30 whilethe dY character is stored therein for mode 3. For mode I, the JXcharacter is stored in the first storage register 128 and the dYcharacter is stored in the second storage register 130 in the presentlypreferred embodiment of the invention. It will be appreciated, however,that other storage assignments could be made for the information to bestored.

When the dX character is received, the P2 signal from the sequencecounter 152 enables the first and second storage registers I28, 130 and,if the system is in mode I the dX character is stored in the firststorage register. However, if the system is in mode 2, the dX characteris stored in the second storage register I30. In mode 4, the dXcharacter is not stored in either storage register, as discussed above.The dX character is simultaneously fed through the dX selection gates112, also enabled by the P2 signal, to the X actuator 122.

When the J! character is received in the input register I10, a P3 signalfrom the sequence counter 152 enables the second storage register I30and the dY selection gates I14. The dY character is stored if the systemis in modes I or 3 and the character is fed to the Y actuator 124through the enabled dY selection gates I14. When the symbol character isreceived in the input register III), the P4 signal from the sequencecounter 152 enables the first storage register 128 to store the symbolif the system is in modes 2, 3 or 4. The P4 signal is also fed to one ofthe control inputs I68 to disable the print suppress section 166 toallow the symbol to be printed.

The mode-quadrant sequence counter 152 then generates a continuous P5signal which is applied to the control inputs I40, 142, I44 of the dX,dY and symbol selection gates I12, IN, I20, respectively, and also toone of the control inputs 168 to the print suppress section 166 tocontinuously enable the gates and disable the print suppress section.The combination of the P5 signal and the mode signal applied at thecontrol inputs I40, 142, 144 of the dX, W and symbol selection gatesI12, H4, 120, respectively, determine whether the respective inputs tothe gates will be taken from the general input line I16, the serialinput line 118, or from one of the storage registers I28, I30.Additionally, a pair of feedback lines 169 interconnect the controlinputs I40, 142 to the 4X and (1! selec tion gates I12, I14,respectively, to condition the gates to alternately receive the incomingvariable character as a dX character and a dY character for mode 4.

The data terminal system of the present invention can be conditioned tooperate substantially like a conventional, controlled teletypewriter bymeans of a text lock 170, which is preferably manually operated. Whenthe text lock 170 is activated, the mode storage section 138, thequadrant storage section 162, the first and second storage registersI28, 130 and the mode-quadrant sequence counter 152, are locked" inappropriate conditions for receiving and printing textual material.

In an alternate coding scheme for the data terminal system of thepresent invention, the mode-quadrant character is restricted toalphabetic characters only and the dX and dY characters are restrictedto the numeric characters. When the transmitted variable is dX or dY,therefore, any alphabetic character which is received can be treated asa mode'quadrant character directly so that no flag character is needed.It will be appreciated that the flag character is then eliminated fromthe character stream for increased speed and economy of time. However,it should be noted that, if the system is operating in mode I, thevariable transmitted could validly be an alphabetic character and theflag signal is needed to change the system from mode 1 to another mode.

FIG. 7 is a partial block diagram of the decoder-controller of FIG. 6and shows an added mode-quadrant character detector I72 controlled bythe mode storage section I36 for receiving character streams using thealternate coding scheme. Basically, the mode-quadrant character detector172 detects alphabetic characters and its effect is equivalent to thatof the flag detector in that it resets the mode-quadrant change sequencecounter 152 (FIGS. 6 and 7) and the operation proceeds as describedabove. If the system is in mode 1, however, the variable charactersreceived by the input register 110 could validly be alphabeticcharacters and the mode-quadrant character detector I72 would generateerroneous rest signals. Therefore, when the system is in mode I, themode storage section 136 disables the mode-quadrant character detector172 and the mode-quadrant change sequence counter 152 can only be resetby the flag detector 150.

FIG. 8 shows an example of a character stream utilizing the alternatecoding stream described above. Initially, a flag character conditionsthe receiver to store the appropriate characters and set the system in aparticular mode. Thus, in the example the second character is a mode 2,quadrant 2 character which sets the system in mode 2. The third, fourthand fifth characters are the dX, dY and symbol characters, as discussedabove. Since the system is in mode 2, all characters received thereafterwill be considered as variable dY characters, such as the sixth,seventh, eighth, and ninth received characters. If a mode change isrequired, only the modequadrant character need be transmitted, such asthe 10th received character, which conditions the system for mode 3,quadrant 2. The llth, 12th and l3th characters are received as dX, ti!and symbol characters, as discussed above. Since the system is in mode3, subsequently received characters are interpreted as variable dXcharacters, such as the 14th, 15th, 16th, 17th and 18th characters.Again, if a mode change is required, only a mode-quadrant character needbe transmitted, such as the 19th character. The 19th mode-quadrantcharacter conditions the system for mode 3, quadrant 3 and the 20th,21st and 22nd character are again interpreted as d)(, if! and symbolcharacters. Since the system remains in mode 3, the subsequentlyreceived 23rd and 24th characters are interpreted again as variable dXcharacters.

The 25th character sets the system for operation in mode 1, quadrant 3and the 26th, 27th, and 28th characters are interpreted dX, dY andsymbol characters. The variable for mode I is the symbol characterwhich, thus far, was considered as a mode-quadrant character. In orderfor the system to operate correctly, the mode-quadrant characterdetector 172 (FIG. 7) is disabled and the system operates as discussedabove with reference to FIG. 6. Therefore, the 29th, 30th and 3 lstcharacters are received normally.

In order to change the system to another mode, a flag character such asthe 32nd character is required before the mode-quadrant character can bereceived. Thus, the 33rd character is a mode 2, quadrant 2 character andthe 34th 35th and 36th characters are dX, (N and symbol characters.Again, since the system is in mode 2, the subsequently received 37th,38th, 39th and 40th characters will all be interpreted as variablecharacters.

The print suppress mechanism in the presently preferred embodiment ofthe present invention is electromechanical in nature and is illustrateddiagrammatically in FIG. 9. Generally, a teletypewriter prints by firstpositioning one of the plurality of symbols on a cylindrical-type head60 which is mounted on a rotatable and vertically movable shaft I74. Thesymbol to be printed is positioned directly opposite the platen 38. Ahammer assembly 176 including a striking pad 178 is mounted adjacent tothe type head 60 and is centrally pivotable about a horizontal shaft Iby means of a cam I82 mounted on a rotating shaft I84. The cam 182 movesa lower end I86 of the hammer assembly 176 against a spring I88 and,when the cam rotates past the end 186 of the hammer assembly, the springpivots the hammer assembly about the shaft 180 so that the striker pad178 forces the type head 60 and interposed ribbon (not shown, seeFIG. 1) into contact with the platen 38 to print the symbol.

As a relatively large amount of time is needed in a teletypewriter toposition the various serially actuated cams and rods which make up thetype head 60 positioning apparatus, the print suppress mechanism in oneembodiment of the present invention includes a solenoid 190 which can beactivated to move a solenoid armature 192 in front of the hammerassembly 176 sometime before the hammer assembly would be actuated tostrike the type head. Sufficient time is afforded to receive acharacter, determine if its significance is other than the symbol to beprinted, and activate the solenoid 190 before the symbol can be printed.

An alternate form of the print suppress mechanism is shown in thepartial block diagram of FIG. it) which is substantially identical tothe block diagram of FIG. 6, except for the addition of a delay shiftregister 194 between the symbol selection gates 120 and the symbolactuator 126. When the symbol selection gates 120 receive the symbolcharacter, it is delayed in reaching the symbol actuator 126 by theshift register 194 until it is determined whether the symbol is to beprinted or not. If not, the print suppress signal inhibits the transferof the character from the delay shift register 194 to the symbolactuator 126.

Thus, the data terminal system described above can print both text and agraphical display at a relatively high speed and with considerablyreduced character redundancy to decrease the amount of computer timerequired for economy. While a particular presently preferred embodimentof the data terminal system of the present invention has been describedin detail above, it will be appreciated that many variations of thebasic system are possible without departing from the spirit and scope ofthe present invention. Therefore, the scope of the invention is not tobe limited except by the following claims.

We claim:

1. A method of communicating data representative of textual material andcoordinates of multiple points on a graph to be plotted, including thesymbol to be placed at each point, to a receiver for printing the textand generating the graphical plot, said method comprising:

analyzing said data on a point-to-point basis to determine incrementaldifference information between points and further determining if any ofsaid information and said symbol is invariable over a plurality ofpoints;

transmitting said information and said symbol to said receiver for onepoint and commanding said receiver to store said invariable information;

generating a graphical plot of said one point whereby the associatedsymbol is placed at the point; and

thereafter transmitting only the variable incremental differenceinformation between points over said plurality of points and taking thecomplete information required for plotting each successive point fromboth the received variable information and the stored invariableinformation.

2. The method defined in claim I wherein:

analyzing said data includes determining the incremental coordinatedifferences between points and the positive or negative signs of suchdifierences based on a rectangular coordinate system; and

combing said signs into a single item of quadrant information indicativeof one of the four quadrants of a rectangular coordinate system, tothereby reduce the number of items of information which must betransmitted to said receiver.

3. The method defined in claim 2 wherein:

said commanding of the storage of invariable information is inaccordance with one of a plurality of mode signals indicative of whichitems of information are to be stored.

4. The method defined in claim 3, and further including:

combining said quadrant information and said one of said plurality ofmode signals into a single mode-quadrant character to reduce the amountof information to be transmitted to said receiver.

5. The method defined in claim I wherein said commanding is inaccordance with one of a plurality of made signals indicative of theparticular invariable items to be stored.

6. A method of communicating data to a receiver with said datarepresenting the coordinate and symbol infonnation for a plurality ofpoints of a graph to be plotted and thereafter generating the graphicalplot, said method comprising:

analyzing said data on a point-to-point basis to determine theincremental coordinate difference information between points, andpositive or negative sign information for said coordinate differenceinformation, required to plot from point-to-point;

comparing the sign, coordinate difference and symbol information withcorresponding items previously stored in said receiver as invariables;determining a proper one of a plurality of modes of operation andgenerating a corresponding mode signal if any of said sign, coordinatedifference and symbol information is different than said correspondinginformation stored in said receiver; transmitting the unstored variableitem of information to the receiver if said items of information are thesame as said corresponding stored items, and thereafter taking thecomplete information necessary to plot the point and symbol from boththe received variable item of information and the stored invariableitems of information; and

transmitting all of said items of information to the receiver togetherwith said mode signal in a character stream in a predetermined order ifat least one of said items of information is different than saidcorresponding stored items of information and storing in said receiverthe appropriate items of information indicated by said mode signal, andthereafter plotting the point and symbol on the graph by taking thecomplete information needed from the received items of information.

7. The method defined in claim 6, and further including:

combining the sign information of said incremental coordinatedifferences into a single item of quadrant information indicative of oneof the four quadrants of a rectangular coordinate system.

8. The method defined in claim 7, and further includin g:

combining said quadrant information and said mode signal into a singleitem of modequadrant information.

9. The method defined in claim 8, and further including:

restricting said mode-quadrant, coordinate difference and symbolinformation to alphanumeric characters for transmission; and

transmitting a nonalphanumeric flag character to said receiver prior totransmitting all of said information to condition said receiver toattach the appropriate sig niiicance to each of the subsequentlyreceived characters in said character stream.

10. The method defined in claim 9, and further including:

selectively conditioning said receiver with one of said mode signals tostore said quadrant and said coordinate difference information andthereafter treat subsequently received characters as symbol informationonly, whereby text material may be received.

ll. The method defined in claim 10, and further including:

generating said graphical plot or said textual material by means of ateletypewriter mechanism having an impact printing-type head carrying afont of symbols which can be printed, the type head carriage and platenof said teletypewriter mechanism being drivable in both positive andnegative directions of movement depending on said quadrant information,whereby the symbols placed at the points of the graphical plot may beany of the font of symbols carried by said type head.

12. The method defined in claim 9, and further including:

generating said graphical plot or said textual material by means of ateletypewriter mechanism having an impact printing-type head carrying afont of symbols which can be printed, the type head carriage and platenof said teletypewriter mechanism being drivable in both positive andnegative directions of movement depending on said information storagemeans in said receiver for storing selected items of coordinatedifference, sign and symbol information designated as invariable;

comparing means for comparing said sign, incremental quadrantinformation whereby the symbols placedat the coordinate difference andsymbol information for each points of the graphical plot may be any ofthe font of symsuccessive point with the corresponding information bolscarried by said type head. stored in said storage means; 13. The methoddefined in claim 8, and further including: transmitting means fortransmitting said coordinate difgenerating said graphical plot or saidtextual material by ference, sign and symbol infonnation to saidreceiver if at means of a teletypewriter mechanism having an impactleast one of said items of information is different than thatprinting-type head carrying a font of symbols which can stored in saidstorage means said transmitting means be printed, the type head carriageand platen f id tale. transmitt ng only the variable item of informationto said typewriter mechanism being drivable in both positive and f lmfolmauon an same as negative directions of movement, depending on saidmvanable salld smrage "l I quadrant information whereby the symbokplaced at the 20. The system defined in claim 19 wherein said comparingpoint of the graphical plot may be any of the font of symmeans Includes:bob M by said type heal mode signal generating means for generating aplurality of 14. The method defined in claim 13, and further including:mode s|gnal mdcat've modes 9 0963mm f 531d conditioning said receiverwith one of said mode signals to system pariucular mode befng generatedstore the quadrant and coordinate difference information 2 cfrdance "Eand and thereafier treat subsequently received characters as dfleFence'and symbol ,nfomauon for each symbol information only, whereby textmaterial may be m F F Mm l' re'suhs of the 2" received parison of saidinformation with said corresponding 15. The method defined in claim 7,and further including: Ftomd mizolimanoni and generating said graphicalplot or said textual material by said "ansmmmg means also "ansmns andmode @315 w means of a teletypewriter mechanism having an impactprinting-type head carrying a font of symbols which can be printed, thetape head carriage and platen of said teletypewriter mechanism beingdriveable in both positive said receiver to condition said receiver tostore the particular items of information associated with particularmode signals.

21. The system as defined in claim 19 wherein said analyzing meanscombines said items of sign information into a single item of quadrantinformation indicative of one of the four quadrants of a rectangularcoordinate system.

and negative directions of movement, depending on said quadrantinformation, whereby the symbols placed at the points of the graphicalplot may be any of the font of symbols carried by said type head. 16.The method defined in claim 15, and further including:

22. The system defined in claim 21 wherein: said comparing meansincludes mode signal generating conditioning said receiver with one ofsaid mode signals to means l mode .signals in i sum: the quadrant andcoordinate difference information predetermined criteria for saidquadrant, coordinate difand thereafter treat subsequently receivedcharacters as farm symbol mformauon m further symbol information only,whereby text material may be cordance results compans?" belween receiveditems of information and said corresponding stored items 17. The methoddefined in claim 6, and further including: 40 P mfOrmatIPm generatingsaid graphical plot and said textual material by Sam system i F "'f fsignal .gene'aung means of a teletypewriter mechanism having an impact,means combmmg l f s'gnal said quadram primins head carrying a font ofsymbols which can information to form a single item of mode-quadrantinforbe printed, the type head carriage and platen of said telel' P P ofr of mformauon typewriter mechanism being drivable in both positive andF fil to Sam recewer i l' and negative directions of movement, dependingon said Sam n'fmsmmm? mean? lransnlns quadrant information, whereby thesymbols placed at the i rece'ver rccc'lfer means for points of thegraphical plot may be any of the font of symf'P fl molie l' quadrant andconbols carried by said we head. ditioning said receiver in accordancewith said mode inm- The method ofclaim 16 and furtherincluding:formation to store particular items of received informaconditioning saidreceiver to store said sign and coordinate m accordance w'th g' i modesdifl'erence information and thereafter treat subsequently The system 22w stem received characters as symbol information only, wherebymode'quadram dlfference and P mformauo are ten material may be received.taken from the group of alphanumeric characters; and

said transmitting means includes a means for generating a 19. A systemfor encoding data for transmission to a flag signal to be transmittedprior to transmitting said mode-quadrant, coordinate difference andsymbol characters to condition said receiver to assign respectivemode-quadrant, coordinate difference and symbol sigreceiver, the databeing indicative of both textual material and the coordinate and pointsymbol information of a plurality of points on a graph to be plotted,said system comprising:

analyzing means for analyzing said data on a point-to-point basis todetermine incremental coordinate difference "i the three reseivedcharacters Said flag items of information between points and the signsS'gnalbeluganomflphanumenccharacer' thereof:

1. A method of communicating data representative of textual material andcoordinates of multiple points on a graph to be plotted, including thesymbol to be placed at each point, to a receiver for printing the textand generating the graphical plot, said method comprising: analyzingsaid data on a point-to-point basis to determine incremental differenceinformation between points and further determining if any of saidinformation and said symbol is invariable over a plurality of points;transmitting said information and said symbol to said receiver for onepoint and commanding said receiver to store said invariable information;generating a graphical plot of said one point whereby the associatedsymbol is placed at the point; and thereafter transmitting only thevariable incremental difference information between points over saidplurality of points and taking the complete information required forplotting each successive point from both the received variableinformation and the stored invariable information.
 2. The method definedin claim 1 wherein: analyzing said data includes determining theincremental coordinate differences between points and the positive ornegative signs of such differences based on a rectangular coordinatesystem; and combining said signs into a single item of quadrantinformation indicative of one of the four quadrants of a rectangularcoordinate system, to thereby reduce the number of items of informationwhich must be transmitted to said receiver.
 3. The method defined inclaim 2 wherein: said commanding of the storage of invariableinformation is in accordance with one of a plurality of mode signalsindicative of which items of information are to be stored.
 4. The methoddefined in claim 3, and further including: combining said quadrantinformation and said one of said plurality of mode signals into a singlemode-quadrant character to reduce the amount of information to betransmitted to said receiver.
 5. The method defined in claim 1 whereinsaid commanding is in accordance with one of a plurality of mode signalsindicative of the particular invariable items to be stored.
 6. A methodof communicating data to a receiver with said data representing thecoordinate and symbol information for a plurality of points of a graphto be plotted and thereafter generating the graphical plot, said methodcomprising: analyzing said data on a point-to-point basis to determinethe incremental coordinate difference information between points, andpositive or negative sign information for said coordinate differenceinformation, required to plot from point-to-point; comparing the sign,coordinate difference and symbol information with corresponding itemspreviously stored in said receiver as invariables; determining a properone of a plurality of modes of operation and generating a correspondingmode signal if any of said sign, coordinate difference and symbolinformation is different than said corresponding information stored insaid receiver; transmitting the unstored variable item of information tothe receiver if said items of information are the same as saidcorresponding stored items, and thereafter taking the completeinformation necessary to plot the point and symbol from both thereceived variable item of information and the stored invariable items ofinformation; and transmitting all of said items of information to thereceiver together with said mode signal in a character stream in apredetermined order if at least one of said items of information isdifferent than said corresponding stored items of information andstoring in said receiver the appropriate items of information indicatedby said mode signal, and thereafter plotting the point and symbol on thegraph by taking the complete information needed from the received itemsof information.
 7. The method defined in claim 6, and further inclUding:combining the sign information of said incremental coordinatedifferences into a single item of quadrant information indicative of oneof the four quadrants of a rectangular coordinate system.
 8. The methoddefined in claim 7, and further including: combining said quadrantinformation and said mode signal into a single item of mode-quadrantinformation.
 9. The method defined in claim 8, and further including:restricting said mode-quadrant, coordinate difference and symbolinformation to alphanumeric characters for transmission; andtransmitting a nonalphanumeric flag character to said receiver prior totransmitting all of said information to condition said receiver toattach the appropriate significance to each of the subsequently receivedcharacters in said character stream.
 10. The method defined in claim 9,and further including: selectively conditioning said receiver with oneof said mode signals to store said quadrant and said coordinatedifference information and thereafter treat subsequently receivedcharacters as symbol information only, whereby text material may bereceived.
 11. The method defined in claim 10, and further including:generating said graphical plot or said textual material by means of ateletypewriter mechanism having an impact printing-type head carrying afont of symbols which can be printed, the type head carriage and platenof said teletypewriter mechanism being drivable in both positive andnegative directions of movement depending on said quadrant information,whereby the symbols placed at the points of the graphical plot may beany of the font of symbols carried by said type head.
 12. The methoddefined in claim 9, and further including: generating said graphicalplot or said textual material by means of a teletypewriter mechanismhaving an impact printing-type head carrying a font of symbols which canbe printed, the type head carriage and platen of said teletypewritermechanism being drivable in both positive and negative directions ofmovement depending on said quadrant information whereby the symbolsplaced at the points of the graphical plot may be any of the font ofsymbols carried by said type head.
 13. The method defined in claim 8,and further including: generating said graphical plot or said textualmaterial by means of a teletypewriter mechanism having an impactprinting-type head carrying a font of symbols which can be printed, thetype head carriage and platen of said teletypewriter mechanism beingdrivable in both positive and negative directions of movement, dependingon said quadrant information, whereby the symbols placed at the point ofthe graphical plot may be any of the font of symbols carried by saidtype head.
 14. The method defined in claim 13, and further including:conditioning said receiver with one of said mode signals to store thequadrant and coordinate difference information and thereafter treatsubsequently received characters as symbol information only, wherebytext material may be received.
 15. The method defined in claim 7, andfurther including: generating said graphical plot or said textualmaterial by means of a teletypewriter mechanism having an impactprinting-type head carrying a font of symbols which can be printed, thetype head carriage and platen of said teletypewriter mechanism beingdriveable in both positive and negative directions of movement,depending on said quadrant information, whereby the symbols placed atthe points of the graphical plot may be any of the font of symbolscarried by said type head.
 16. The method defined in claim 15, andfurther including: conditioning said receiver with one of said modesignals to store the quadrant and coordinate difference information andthereafter treat subsequently received characters as symbol informationonly, whereby text material may be received.
 17. The method defined inclaim 6, and further including: generating said graphical plot and saidtExtual material by means of a teletypewriter mechanism having an impactprinting-type head carrying a font of symbols which can be printed, thetype head carriage and platen of said teletypewriter mechanism beingdrivable in both positive and negative directions of movement, dependingon said quadrant information, whereby the symbols placed at the pointsof the graphical plot may be any of the font of symbols carried by saidtype head.
 18. The method of claim 16, and further including:conditioning said receiver to store said sign and coordinate differenceinformation and thereafter treat subsequently received characters assymbol information only, whereby text material may be received.
 19. Asystem for encoding data for transmission to a receiver, the data beingindicative of both textual material and the coordinate and point symbolinformation of a plurality of points on a graph to be plotted, saidsystem comprising: analyzing means for analyzing said data on apoint-to-point basis to determine incremental coordinate differenceitems of information between points and the signs thereof; informationstorage means in said receiver for storing selected items of coordinatedifference, sign and symbol information designated as invariable;comparing means for comparing said sign, incremental coordinatedifference and symbol information for each successive point with thecorresponding information stored in said storage means; transmittingmeans for transmitting said coordinate difference, sign and symbolinformation to said receiver if at least one of said items ofinformation is different than that stored in said storage means, saidtransmitting means transmitting only the variable item of information tosaid receiver, if said items of information are the same as thoseinvariable items stored in said storage means.
 20. The system defined inclaim 19 wherein said comparing means includes: mode signal generatingmeans for generating a plurality of mode signals indicative of modes ofoperation for said system, particular mode signals being generated inaccordance with predetermined criteria for said coordinate difference,sign and symbol information for each point and in further accordancewith the results of the comparison of said information with saidcorresponding stored information; and said transmitting means alsotransmits said mode signals to said receiver to condition said receiverto store the particular items of information associated with particularmode signals.
 21. The system as defined in claim 19 wherein saidanalyzing means combines said items of sign information into a singleitem of quadrant information indicative of one of the four quadrants ofa rectangular coordinate system.
 22. The system defined in claim 21wherein: said comparing means includes mode signal generating means forgenerating mode signals in accordance with predetermined criteria forsaid quadrant, coordinate difference and symbol information and infurther accordance with the results of the comparison between said itemsof information and said corresponding stored items of information; saidsystem includes mode-quadrant signal generating means for combining saidmode signal with said quadrant information to form a single item ofmode-quadrant information, whereby the number of items of informationtransmitted to said receiver is reduced; and said transmitting meanstransmits said mode-quadrant information to said receiver, said receiverhaving means for separating said mode and quadrant information andconditioning said receiver in accordance with said mode information tostore particular items of received information in accordance withparticular modes.
 23. The system of claim 22 wherein: saidmode-quadrant, difference and symbol information are taken from thegroup of alphanumeric characters; and said transmitting means includes ameans for generating a flag signal to be transmitted prior totransmitting said mOde-quadrant, coordinate difference and symbolcharacters to condition said receiver to assign respectivemode-quadrant, coordinate difference and symbol significance to the nextthree received characters, said flag signal being a nonalphanumericcharacter.